1. Field of the Invention
The present invention relates to a feed horn of a satellite communication reception converter receiving satellite communication waves, a fabrication method thereof, and a converter for satellite communication reception.
2. Description of the Background Art
FIG. 10 is a perspective view of a satellite broadcast receiving antenna. Broadcast waves from a satellite are reflected at a parabolic antenna 50 and enter a feed horn 10 of a satellite broadcast reception converter 1 to be guided through feed horn 10. The guided satellite broadcast waves are applied to a converter circuit arranged in satellite broadcast reception converter 1 to be converted into television picture signals and audio signals for output to a television set.
FIGS. 11A and 11B are a sectional view and a front view, respectively, of a conventional satellite broadcast reception converter. Referring to FIGS. 11A and 11B, satellite broadcast reception converter 1 includes shield cases 2 and 3 to protect internal components. Converter 1 has a printed circuit board 4 attached therein. A converter circuit converting satellite broadcast waves into electric signals is implemented on printed circuit board 4. A feed horn 10 receiving satellite broadcast waves is attached to the outer side of shield case 2. An F type attachment 8 to output an electric signal towards a television set is provided at a predetermined region of shield cases 2 and 3 so as to protrude outwards.
Feed horn 10 is formed of a tubular member having a transmission path configured therein through which satellite broadcast waves are guided. At the satellite broadcast wave input side of feed horn 10, a horn cap 7 to maintain a sealed interior is attached. This horn cap 7 is formed of a material other than a conductor so as to pass through at least satellite broadcast waves.
The other end side of feed horn 10 is coupled to printed circuit board 4 mounted in shield cases 2 and 3. As shown in FIG. 11B, probes 5 and 6 corresponding to the antenna unit are provided at a region of printed circuit board 4 facing the transmission path of feed horn 10.
According to the above structure, satellite broadcast waves entering feed horn 10 through horn cap 7 are guided through feed horn 10 to arrive at probes 5 and 6 located at printed circuit board 4. The satellite broadcast waves received by probes 5 and 6 are converted into television picture signals and audio signals by the converter circuit provided on printed circuit board 4 and output towards a television set via F type attachment 8.
It is appreciated from the drawings that feed horn 10 of the satellite broadcast reception converter of the above structure is attached to shield cases 2 and 3 with the outer circumferential plane exposed. From the aesthetical standpoint, the outer circumferential plane of feed horn 10 must be configured with an ornamental plane to improve the appearance. The inner circumferential plane of feed horn 10 must allow the satellite broadcast wave arriving at the transmission path in feed horn 10 through horn cap 7 to be transmitted to probes 5 and 6 provided at printed circuit board 4 without any loss. This means that the inner circumferential plane of feed horn 10 must have a waveguide plane formed of, for example, a conductor, provided thereon.
FIG. 12 shows a sectional view of a conventional feed horn of a converter for satellite broadcast reception. Referring to FIG. 12, a conventional feed horn 10E has its frame formed of a resin member 11. In order to comply with the above-described requirements, a metal plate layer 12 corresponding to a waveguide plane is formed on the inner circumferential plane of resin member 11. On the outer circumferential plane of resin member 11, a coating layer 13 which is the ornamental plane is disposed.
Feed horn 10E with a metal plate layer 12 on the inner circumferential plane and a coating layer 13 on the outer circumferential plane is fabricated as set forth below. First, as shown in FIG. 13, a tubular resin member 11 corresponding to the frame of feed horn 10E is formed by injection molding. Then, metal plating is applied all over resin member 11. Accordingly, the entire surface of resin member 11 is covered with a metal plate layer 12, as shown in FIG. 14. Then, the inner circumferential plane of resin member 11 covered with metal plate layer 12 is masked, followed by coating via a spray gun. Accordingly, a coating layer 13 is selectively formed only at the outer circumferential plane of resin member 11 that was not masked. The mask is then removed, resulting in feed horn 10 of the structure shown in FIG. 12.
For the resin member, an acrylo nitrile-butadiene-styrene (ABS) resin, for example, is employed to allow metal plating. For the coating composition, acrylic based coating is employed.
The above-described fabrication method of a feed horn for a satellite broadcast reception converter is disadvantageous in that the fabrication process is complicated due to the requirement of masking in the coating step, resulting in increase of the fabrication cost. Furthermore, the resin material that can be used to form the resin member was limited to resin materials that allow metal plating. There was a problem that the selection range of materials is small.